Lib/plat-irix5/panelparser.py

   1 # Module 'parser'
   2 #
   3 # Parse S-expressions output by the Panel Editor
   4 # (which is written in Scheme so it can't help writing S-expressions).
   5 #
   6 # See notes at end of file.
   7 from warnings import warnpy3k
   8 warnpy3k("the panelparser module has been removed in Python 3.0", stacklevel=2)
   9 del warnpy3k
  10
  11
  12 whitespace = ' \t\n'
  13 operators = '()\''
  14 separators = operators + whitespace + ';' + '"'
  15
  16
  17 # Tokenize a string.
  18 # Return a list of tokens (strings).
  19 #
  20 def tokenize_string(s):
  21     tokens = []
  22     while s:
  23         c = s[:1]
  24         if c in whitespace:
  25             s = s[1:]
  26         elif c == ';':
  27             s = ''
  28         elif c == '"':
  29             n = len(s)
  30             i = 1
  31             while i < n:
  32                 c = s[i]
  33                 i = i+1
  34                 if c == '"': break
  35                 if c == '\\': i = i+1
  36             tokens.append(s[:i])
  37             s = s[i:]
  38         elif c in operators:
  39             tokens.append(c)
  40             s = s[1:]
  41         else:
  42             n = len(s)
  43             i = 1
  44             while i < n:
  45                 if s[i] in separators: break
  46                 i = i+1
  47             tokens.append(s[:i])
  48             s = s[i:]
  49     return tokens
  50
  51
  52 # Tokenize a whole file (given as file object, not as file name).
  53 # Return a list of tokens (strings).
  54 #
  55 def tokenize_file(fp):
  56     tokens = []
  57     while 1:
  58         line = fp.readline()
  59         if not line: break
  60         tokens = tokens + tokenize_string(line)
  61     return tokens
  62
  63
  64 # Exception raised by parse_exr.
  65 #
  66 syntax_error = 'syntax error'
  67
  68
  69 # Parse an S-expression.
  70 # Input is a list of tokens as returned by tokenize_*().
  71 # Return a pair (expr, tokens)
  72 # where expr is a list representing the s-expression,
  73 # and tokens contains the remaining tokens.
  74 # May raise syntax_error.
  75 #
  76 def parse_expr(tokens):
  77     if (not tokens) or tokens[0] != '(':
  78         raise syntax_error, 'expected "("'
  79     tokens = tokens[1:]
  80     expr = []
  81     while 1:
  82         if not tokens:
  83             raise syntax_error, 'missing ")"'
  84         if tokens[0] == ')':
  85             return expr, tokens[1:]
  86         elif tokens[0] == '(':
  87             subexpr, tokens = parse_expr(tokens)
  88             expr.append(subexpr)
  89         else:
  90             expr.append(tokens[0])
  91             tokens = tokens[1:]
  92
  93
  94 # Parse a file (given as file object, not as file name).
  95 # Return a list of parsed S-expressions found at the top level.
  96 #
  97 def parse_file(fp):
  98     tokens = tokenize_file(fp)
  99     exprlist = []
 100     while tokens:
 101         expr, tokens = parse_expr(tokens)
 102         exprlist.append(expr)
 103     return exprlist
 104
 105
 106 # EXAMPLE:
 107 #
 108 # The input
 109 #       '(hip (hop hur-ray))'
 110 #
 111 # passed to tokenize_string() returns the token list
 112 #       ['(', 'hip', '(', 'hop', 'hur-ray', ')', ')']
 113 #
 114 # When this is passed to parse_expr() it returns the expression
 115 #       ['hip', ['hop', 'hur-ray']]
 116 # plus an empty token list (because there are no tokens left.
 117 #
 118 # When a file containing the example is passed to parse_file() it returns
 119 # a list whose only element is the output of parse_expr() above:
 120 #       [['hip', ['hop', 'hur-ray']]]
 121
 122
 123 # TOKENIZING:
 124 #
 125 # Comments start with semicolon (;) and continue till the end of the line.
 126 #
 127 # Tokens are separated by whitespace, except the following characters
 128 # always form a separate token (outside strings):
 129 #       ( ) '
 130 # Strings are enclosed in double quotes (") and backslash (\) is used
 131 # as escape character in strings.